It is known to use snap-acting discs having a dished-shape configuration as fluid pressure sensors to control the energization of an electric circuit in response to selected fluid pressure conditions. Such discs are typically mounted in a recess formed in a housing in pressure receiving relation with a fluid pressure source sealed from the fluid as by a flexible flat membrane disposed over the recess and attached to the housing. An electric switch is mounted in the housing having a movable contact mounted on a movable contact arm and adapted to move into and out of engagement with a stationary contact and with an elongated motion transfer pin either directly attached to the movable arm or mounted in a guide hole placed between the movable arm and the disc so that when the disc snaps from one configuration to an oppositely dished configuration upon the occurrence of a selected pressure condition of the fluid pressure source being monitored, motion is transferred from the disc to the movable arm to move the movable contact either into or out of engagement with the stationary contact.
In certain markets, due to competitive reasons, there is a continuing need to minimize the cost of the pressure switch and at the same time to maximize the expected useful life of the switch. Failure modes of switches of the type described include fatigue of the sealing membrane used to transfer pressure from the fluid to the disc exacerbated by the repetitious stretching of the membrane in a direction perpendicular to the surface of the membrane in its weakest direction. Another failure mode occurs in switches having free motion transfer pins which often develop contamination in the switch cavity from the wearing of parts. Another cause of failure of switches having normally free discs occurs when such a disc becomes trapped in a skewed orientation in a disc receiving recess of the housing.